唇亡齿寒（唇亡齒寒|脣亡齒寒）　

◎ 唇亡齿寒 chúnwáng-chǐhán

[mutual dependency of neighboring countries when confronted with a powerful and aggressive enemy;share a common lot] 唇没有了,牙齿就寒冷。比喻双方休戚相关,荣辱与共